Omalium curtipenne Mäklin, 1878

Shavrin, Alexey V., 2025, Review of the genus Omalium Gravenhorst, 1802 (Coleoptera: Staphylinidae: Omaliinae: Omaliini) of Siberia and Far Eastern Russia, with notes on some species from Mongolia and Japan, Zootaxa 5646 (2), pp. 199-235 : 213-217

3.2.4.2. Omalium curtipenne Mäklin, 1878

( Figs 10–11 , 23 , 25–28 , 31 )

Homalium curtipenne Mäklin, 1878: 30 ; J. Sahlberg 1880: 110, Mäklin 1881: 44.

Omalium curtipenne : Luze 1906: 514, Poppius 1904b: 4, Kashcheev 1999: 142.

Omalium (Omalium) curtipenne : Bernhauer & Schubert 1910: 52.

Omalium lacki Bernhauer, 1940: 625 syn. nov.

Type material examined. Holotype of Homalium curtipenne Mäklin, 1878 ♂: ‘Dudino’ <printed>, ‘Sibir’ <printed>, ‘Jeniseie’ <printed>, ‘curtipenne | Mäklin’ <handwritten in black>, ‘7164 E91+’ <blue, printed>, ‘probably type [handwritten] M.K. Thayer 2010’ <printed> (SMNH).

Lectotype (here designated) of Omalium lacki Bernhauer, 1940 ♂ (dissected): ‘ Bear Island : Fugleodden. | 13.vii. [handwritten in black] 1932.’ <printed>, ‘ D. Lack. | B.M. 1932-378.’ <printed>, ‘Arct. Ocean | Bären Insel | Brit. Museum’ <handwritten in black>, ‘lacki Brh | Type.’ <handwritten in black>, ‘Lacki Brnh | Type | Omalium’ <red, handwritten in black>, ‘Chicago NHMus | M.Bernhauer | Collection’ <printed>, ‘ Syntype | lacki Bernh. | det. M.K. Thayer 19[printed]90’ <handwritten in black>, ‘ SYNTYPE | teste D.J.Clarke2014 | GDI Imaging Project’ <violet, printed>, ‘PHOTOGRAPHED | Kelsey Keaton 2014 | Emu Catalog’ <blue, printed>, ‘FMNHINS | 2819646 | FIELD MUSEUM’ <printed, with barcode on left side of the label>, ‘ LECTOTYPE | Omalium | lacki Bernhauer, 1940 | Shavrin A.V. des. 2025’ <red, printed>, ‘ Omalium | curtipenne Mäklin, 1878 | Shavrin A.V. det. 2025’ <printed> (FMNH).

Paralectotypes: 1 ♀: ‘ Bear Island : Fugleodden. | 5.viii. [handwritten in black] 1932.’ <printed>, ‘ D. Lack. | B.M. 1932-378.’ <printed>, ‘BRIT. MUS. | DON. ARROW’ <printed>, ‘Lacki Brnh | Type | Omalium’ <red, handwritten in black>, ‘Chicago NHMus | M.Bernhauer | Collection’ <printed>, ‘Syntype | lacki Bernh. | det. M.K. Thayer 19[printed]90’ <handwritten in black>, ‘SYNTYPE | teste D.J.Clarke2014 | GDI Imaging Project’ <violet, printed> ( FMNH) ; 1 ♂: ‘ Bear Island : | Fagleodden. | 5.VIII. [handwritten] 1932.’ <printed>, ‘ D. Lack. | B.M. 1932- 378.’ <printed>, ‘ W.Steel coll. | B.M. 1969-552.’ <printed> ( BMNH) ; 1 ♀ (right antenna missing): ‘ Bear Island : | Fugleodden. | 8.VII. [handwritten] 1932. | D. Lack. | B. M. 1932-378.’ <printed> ( BMNH). All paralectotypes with additional labels: ‘ Paralectotype’ <red, printed>, ‘ Omalium | curtipenne Mäklin, 1878 | Shavrin A.V. det. 2025’ <printed>.

The photographs of the habitus and type labels are also available in Arthropod Collections Database of FMNH (last access: 24.04.2025).

Material examined. TYUMEN AREA: 1 ♀: Uvatskiy District, 10 km S Gornoslinkino, near Tobolsk Field Research Station of Severtsov Institute, near mouth of Varpak River . Clay bank of river: near water and among sedges. 12.09.2003. A.B. Ryvkin leg. (cSh); KRASNOYARSK TERRITORY: 1 ♂: Turukhanskiy District, Central Siberian State Reserve, middle reaches of Bol`shaya Raskosaya River . Pleurozium schreberi , Hylocomium splendens etc. in forest with Picea obovata, Betula sp., Pinus sibirica , Abies sibirica , Juniperus sp. , Larix sibirica , Vaccinium vitis-idaea and V. myrtillus . 24.05.1992. V.B. Semenov leg. (ZMM); 1 ♂: same data, Bolshaya Varlamovka River, middle reaches of Bol`shaya Raskosaya River . 23.05.1992. (cSh); 1 ♂: same Reserve, Stolbovaya River basin: lower reaches of Birapchana River near Kruten`kiy stream. 110 m a.s.l., drift in willow bushes at rill bank. 26.06.1993. V.B. Semenov leg. (cSh); 2 ♀♀: same data, Stolbovaya River basin near mouth of Kruten`kiy stream. 110 m a.s.l., loamy river bank with Salix sp. , dead Poaceae gen. spp. etc., in drift 23.06.1993 (ZMM); 1 ♀: Turukhanskiy District, Nizhnyaya Sarchikha River near Kamenka River mouth. 150 m a.s.l., under mosses near bank of the river. 06– 07.07.1992. V.B. Semenov leg. (cSh); 1 ♀: same District, Mirnoye. Soil traps. 05– 15.08.1989. L.B. Rybalov leg. (ZMM); 8 ♂♂, 9 ♀♀: same data. 06– 20.07.1990. (cSh, ZMM); 1 ♀: ‘ Nikandrovski insula 70º40’’, ‘2190’, ‘7165 E91+’, ‘curtipenne Mäkl. ’ (SMNH); EVENKIA: 3 ♂♂, 2 ♀♀: Baykitskiy District, Bol`shoy Baykitik River, 1–3 km up-stream Baykit. 150 m a.s.l., mosses at bank of the river. 21.09.1993. A.B. Ryvkin leg. (cSh, ZMM); 2 ♂♂: same District, basin of left tributary of Bol`shoy Baykitik River near Baykit. 180 m a.s.l., mosses and litter at bank of stream under Picea obovata , Larix? czekanowskii, Betula sp., Salix sp. , Alnus sp. , with Sphagnum spp. , Plagiomnium spp. , Pleurozium schreberi , Hylocomium splendens , grasses, Linnaea borealis , Vaccinium vitis-idaea , Rosa sp. , Ledum sp. , Chamaedaphne calyculata etc. 02.10.1993. A.B. Ryvkin leg. (cR); 1 ♂: same data. 150 m a.s.l., mosses and litter at bank of stream with sparse Betula sp. , Salix sp. , Alnus sp. , young Picea obovata , grasses etc. 30.09.1993. (cSh); 1 ♀: same District, 3 km up-stream of Baykit. 160–170 m a.s.l., river bank with hummocks: mosses, litter and drift among Salix spp. , Alnus sp. , Betula? fruticosa with Calamagrostis sp. , Carex spp. , Filipendula ulmaria , Equisetum sp. etc. at bottom of stony slope. 26.09.1993. A.B. Ryvkin leg. (cR); 1 ♂: same District, Podkamennaya Tunguska River, environs of Kuz’movka village , Kuz’movskiy Rill. 60 m a.s.l., moss and litter on slope near the rill: Picea obovata , Abies sibirica , Larix sibirica , Salix sp. , Alnus sp. , Lonicera altaica , Ribes sp. , Equisetum sp. , Vaccinium vitis-idaea , V. myrtillus , sparse Betula , Hylocomium splendens , Pleurozium schreberi etc. 12.08.1989. A.B. Ryvkin leg. (cSh); TUVA: 1 ♀: Todzhenskiy District, Toora-Khem village. 900 m a.s.l. Evening flying in the yard and in the garden. 04.06.1992. A.B. Ryvkin leg. (cR); 2 ♂♂, 1 ♀: Mongun-Tayginskiy District, Khindig-Khol` Lake. 2600 m a.s.l., half-ruined rocky outliers, in nests of Alticola strelzowi . 02.09.1984. (ZMM); IRKUTSK AREA: 4 ♂♂: Bodaibinskiy District, Vitimskiy Nature Reserve, Oron Lake , upper flow of right tributary of Pravaya Polovinka (left bank), 57°07.446’N 116°37.131’E. Valley of river with Picea and Betula . 07.06.2015. I.V. Enushchenko leg. (cSh); 2 ♂♂, 1 ♀: same data, right bank of Pravaya Polovinka River , 57°07.360’N 116°36.692’E, ~ 500 m downstream of second rigth tributary. 08.06.2015. I.V. Enushchenko leg. (cSh); 1 ♀: same data, Oron Lake , cordon, 57°11’29.2’’N 116°26’19.6’’E. 67 m a.s.l., swampy bed of stream flowing to the lake. 18.07.2016. I.V. Enushchenko leg. (cSh); CHITA AREA: 1 ♀: Kalarskiy District, Udokan Mts., right side of Sredniy Sakukan River , mouth of Medvezhiy Stream. 22.07.2014. I.V. Enushchenko leg. (cSh); YAKUTIA : 1 ♂, 1 ♀: Suntar-Khalta Mts., valley of Tyry River, Nezhdanskoye , Kidyrki River near Khalya River . 800–950 m a.s.l. 11– 18.08.1991. S.K. Alekseev leg. (cSh); MAGADAN AREA: 1 ♂: Magadan. Alnus forest. 19.08– 18.09.1980. S.P. Bukhkalo leg. (cSh); 1 ♂: Ten`kinskiy District, basin of Detrin River, Vakkhanka Rill (near ford). Soil traps. 28.06– 06.07.1983. S.P. Bukhkalo leg. (cSh); 1 ♂: Khasynskiy District, right bank of Dukcha River , 59°37’52.0’’N 150°56’04.3’’. 104 m a.s.l. 04.06.2016. I.V. Enushchenko leg. (cSh); CHUKOT AUTONOMOUS REGION: 1 ♀: Wrangel Island, Nalednoye Swamp. Soil traps. 02– 13.06.1983. S.P. Bukhkalo leg. (ZMM); AMUR AREA: 1 ♀: Zeyskiy District, Zeyskiy Nature Reserve, left side of Bol’shaya Erakingra River NE of 52nd km cordon, N 54.09080° E 126.87963°. 623 m a.s.l., mosses and litter on/among stones in dry channel. 21.08.2016. A.B. Ryvkin leg. (cSh).

Redescription. Measurements (n=50): HW: 0.47–0.64; HL: 0.35–0.43; OL: 0.12–0.19; TL: 0.06–0.10; AL (averaged): 1.17; PL: 0.43–0.52; PWmax: 0.70–0.79; PWmin: 0.65–0.74; ESL: 0.70–1.02; EW: 0.92–1.01; MTbL (averaged): 0.55; MTrL (averaged): 0.26 (MTrL 1–4: 0.10; MTrL 5: 0.15); AW: 0.93–1.13; AedL: 0.62–0.72; BL: 2.25–3.70 (lectotype of O. lacki : 3.15).

Habitus as in Fig. 23 . Body yellowish-brown to reddish-brown, with paler elytra (some specimens with markedly paler lateral and basal margins of pronotum); antennomeres 5–11 or 6–11 brown; mouthparts, antennomeres 1–4 or 1–5 and legs yellow to yellow-brown (tarsi usually paler). Punctation of head irregular, moderately fine, denser in middle, clypeus without or with fine and sparse punctation; neck with fine and sparse punctation; pronotum with moderately dense punctation, about as that in middle part of head or slightly larger and deeper, sometimes finer and sparser in medioapical and sparser in mediobasal and lateral portions; punctation of elytra denser, larger and deeper than that on pronotum, denser around scutellum, finer and sparser along suture; abdominal tergites with indistinct and fine punctation, sometimes invisible in some specimens. Head with dense and coarse microsculpture: transverse on clypeus, diagonal on laterobasal parts of clypeus and infraorbital portions, sometimes isodiametric between lateral parts of clypeus and eye, and longitudinal and subdiagonal in middle portion; neck with transverse microsculpture, sometimes invisible in middle; pronotum without or with fine isodiametric or longitudinal microreticulation of traces of it in middle portion (some specimens with isodiametric or longitudinal microsculpture in latero-basal portions); scutellum with dense isodiametric meshes; elytra without microreticulation; abdomen with dense isodiametric microsculpture. Anterior part of clypeus with several erect moderately long setae; abdominal tergites with fine and relatively dense setation; posterior margin of pronotum with row of short cuticular fringe, invisible in some specimens.

Head 1.3–1.4 times as broad as long, flattened or slightly elevate in middle, with wide clypeus and slightly explanate supra-antennal elevations; anteriomedian depressions wide, shallow or moderately deep, reaching level of anterior third or middle of eyes; each posteriolateral margin of clypeus diagonally stretching posteriad toward level of anterior third or middle of eye. Mediodorsal surface without or with distinct diagonal or longitudinal elevations between punctures, each infraorbital portion near eye and its posterior part with three to five longitudinal irregular wrinkles, indistinct in some specimens. Anteocellar fovae oval, deep and relatively short, but sometimes elongate and slightly convergent latero-apicad toward level of posterior third or middle of eyes. Temples twice as long as longitudinal length of eye. Nuchal constriction wide and deep. Distance between ocelli 1.7 times to slightly more than twice as long as distance between ocellus and posterior margin of eye. Antennomeres 7–10 slightly transverse; basal antennomere about two and a half to three times as long as broad, antennomere 2 distinctly narrower and shorter than basal antennomere, 3 slightly longer and narrower than 2, 4 small, about twice shorter than 3, 5 slightly loger and broader than 4, 6–7 slightly broader than 5, 8 distinctly broader than 7, 9–10 slightly longer and broader than 8, apical antennomere 1.3–1.5 times as long as preceding segment.

Pronotum distinctly convex, 1.5–1.6 times as broad as long, 1.2–1.4 times as broad as head, widest in or slightly above middle, more narrowed posteriad (gradually or strongly) than anteriad toward obtuse or subacute hind angles. Lateral portions widely impressed, slightly or distinctly explanate, especially in middle and lateral portions in some specimens, each with deep and elongate depressions behind middle. Surface of disc with two shallow or moderately deep elongate longitudinal depressions, without or with indistinct oval medioapical depression; each lateroapical portion with curved narrow elevation, reaching middle of pronotum; surface between all pronotal depressions not or slightly elevated. Middle portion without or with irregular and indistinct diagonal elevations between punctures.

Elytra slightly or disitnctly broader than long, 1.6–1.9 times as long as pronotum, slightly or strongly broadened posteriad. Dorsal surface of each elytron with strong irregular transverse and diagonal elevations between punctures.

Male. Posterior margin of abdominal tergite VIII truncate or indistinctly concave. Posterior margin of abdominal sternite VIII truncate or somewhat rounded. Aedeagus with broadened basal portion, gradually narrowed toward middle; median lobe narrow, elongate, with small rounded apex, from about middle with narrow rounded lateral projections; mediolateral portions with relatively long and narrow sclerotized accessory plates, slightly curved latero-apicad, each rounded apically; parameres wide, significantly shorter than apex of median lobe, each narrowed and curved in preapical portion, with four moderately long apical setae; internal sac relatively narrow, long, with two elongate sclerotized structures in basal portion (invisible in some specimens) ( Figs 25, 27 ). Lateral aspect of the aedeagus as in Fig. 26 ; apical portion of median lobe relatively narrow, with rounded apex, distinctly crenulate ventrodorsally ( Figs 26, 28 ).

Female. Posterior margin of abdominal tergite VIII straight. Posterior margin of abdominal sternite VIII straight or slightly rounded. Accessory sclerite moderately long and wide, from widest basal portion gradually narrowed toward apex ( Fig. 10 ). Spermatheca as in Fig. 11 .

Comparative notes. Based on the general shape of the habitus and the aedeagus, O. curtipenne is somewhat similar to the Holarctic O. strigicolle , from which it can be distinguished by the finer punctation of the head and the pronotum, slightly more transverse pronotum, which is stronger narrowed posteriad from the middle, the shorter elytra, narrower median lobe with presence of narrow lateral projections in about middle and distinctly more narrowed apex, the lack of the lateroapical hook in apical portion of the medion lobe (if viewed laterally), the shape of the female accessory sclerite and other details of the morphology of the aedeagus.

Distribution. Omalium curtipenne is widely distributed in the Palaearctic region from Norway to Far Eastern Russia; faunistic records between Scandinavia and western Siberia are unknown ( Fig. 31 ).

Bionomics. Omalium curtipenne inhabits mixed coniferous-deciduous forests with Picea , Pinus , Abies , Larix, Betula , etc. It most often is found in wet habitats near streams and rivers and can be sifted from mosses, litter and drift. Some specimens were collected in swampy habitats; occasionally it inhabits nests of rabbits and can be collected flying in the evening. The species is recorded from elevations between 60 m a.s.l. to 2600 m a.s.l. The beetles were collected from May to November.

Remarks. Homalium curtipenne was described based on the holotype from “Dudino (lat. bor. 69°15´)…”. This specimen was found in the collection of SMNH (see above).

Omalium lacki was originally described from “…Bären-Insel im nördlichen Eismeer (Fugleodden) [the southernmost island of the Norwegian Svalbard archipelago, Norway]” based on an unspecified number of syntypes. These specimens were collected by “… D. Lack in der Zeit vom 13. Juli 1932 bis 5. August 1932 …” ( Bernhauer 1940). I have studied four syntypes from FMNH and BMNH, and one male from FMNH was designated as the lectotype in order to fix the identity of the species. Based on the general shape of the body and morphology of the aedeagus ( Figs 27–28 ), it is conspecific with specimens of O. curtipenne from Siberia and Far Eastern Russia. Thus, I synonymized O. lacki with it.

Omalium curtipenne was recorded from Krasnoyarsk Territory (J. Sahlberg 1880), Irkutsk Area ( Shavrin 2007), Buryatia ( Eppelsheim 1893, Shavrin 2010) and Chukot Autonomous Region ( Ryabukhin 1999). It was recorded by Shavrin (2010) as O. caesum from Kamennyi Dubches (Krasnoyarsk Territory).

Additional material both for O. curtipenne and O. lacki from Scandinavia and northern European regions of Russia is unknown. It is likely that some published records of O. strigicolle or related species from these regions should be re-studied, especially for the aedeagi in lateral position. The apical portion of the aedeagus of O. curtipenne in lateral position is not forming a hook and is slightly crenulate ventrodorsally (compare Figs 26, 28 , Fig. 53i in Zanetti (2011), and Fig. 49 ). It should also be taken into account that O. curtipenne is variable in some details and proportions of the forebody: somewhat different shape of the anteocellar foveae, the shape of the pronotum can be slightly or more narrowed posteriad, with less or more flattened and explanate lateral portions, elytra can be somewhat shortened or elongate, etc. Despite this, the shape of the aedeagus is not so variable and can be confidently used for species identification. Also see the key below.

It is here recorded from Tyumen Area, Evenkia, Yakutia , Amur, Chita and Magadan areas for the first time.

Figures

FIGURE 31. Distribution of Omalium curtipenne in the Palaearctic region.

FIGURES 10–19. Female accessory sclerite (Figs 10, 12, 14–19) and spermatheca (Figs 11, 13) of Omalium: 10–11—O. curtipenne, 12–13—O. diffine, 14—O. golovatchi, 15—O. japonicum, 16—O. kurilicum, 17—O. longicorne, 18—O. strigicolle, 19—O. subsolanum. Scale bar: 0.1 mm.

FIGURES 22–24. Habitus of Omalium: 22—O. septentrionis (Russia: TyumenArea, Ugut), 23—O. curtipenne (Russia: Irkutsk Area, Vitim Nature Reserve), 24—O. diffine (holotype). Scale bar: 1.0 mm.

FIGURES 25–30. Aedeagus of Omalium (Figs 25–28—O. curtipenne (Figs 25–26—Russia: Magadan Area, Dukcha; Figs 27–28—O. lacki, lectotype), Figs 29–30—O. kurilicum (holotype)): 25, 27, 29—aedeagus, parameral view, 26, 30—aedeagus, lateral view, 28—apical part of median lobe, lateral view. Scale bar: 0.1 mm.

FIGURES 44–49. Aedeagus of Omalium (Figs 44–47—O. subsolanum (Figs 44–45—Russia: Buryatia, valley of Irkut River; Figs 46–47—Japan:Ashiyasu-mura), Figs 48–49—O. strigicolle (Russia:AmurArea, Norskiy Reserve)): 44, 46, 48—aedeagus, parameral view, 45, 49—aedeagus, lateral view, 47—apical part of median lobe, lateral view. Scale bar: 0.1 mm.